The present invention broadly relates to a new and improved construction of an apparatus for detecting and processing sonic or acoustic radiation or energy.
In its more specific aspects the present invention relates to a new and improved construction of a sonic apparatus for motion and foreign body detection in short-range surveillance applications, comprising a source of acoustic or sonic radiation or energy driven by a driver circuit, and including a processing or evaluation circuit which, upon movement of an object, or in the presence of a stationary foreign object which is more solid than ambient air within a monitored space, triggers an alarm signal.
In other words, the short-range surveillance device of the present invention is of the type comprising at least one source of sonic energy having a membrane and a main direction of radiation, a driver circuit for driving the at least one source of sonic energy and an evaluation circuit for emitting an alarm signal in response to motion and/or sojourn within a surveillance space of an object more solid than ambient air.
The method aspects of the present invention for monitoring a surveillance space comprise the steps of employing a driver circuit for driving at least one source of sonic energy having an impedance.
A similar intrusion detector is described in German Patent No. 2,237,613. A sonic source is driven continuously at a constant frequency corresponding to the resonant frequency of a space. This known embodiment of a detector is, however, afflicted with the disadvantage of being operable only within enclosed spaces. Furthermore, the volume of the space must be closely estimated and openings, such as doors, windows, ventilators or cracks must be taken into consideration. This procedure is necessary in order to be able to tune to the space's resonant frequency. This known detector can only operate as a surveillance apparatus if its sonic source emits radiation at the resonant frequency of the space in question. Its installation is arduous, time-consuming and requires specially trained personnel. If the resonant frequency changes or is altered during service, i.e., by changes in the spaces's volume or changes of the space's apertures, this known detector will generate false alarms. Another disadvantage of this known. detector consists in its tendency to trigger false alarms due to the presence of laminar or turbulent air currents or due to insects flying within the monitored space.